'Victor IV' was the US and Filipino seizure of the Zamboanga peninsula on the western tip of Mindanao island in the Philippine islands group by units of Major General Jens A. Doe’s 41^st Division of Lieutenant General Robert L. Eichelberger’s 8^th Army (10/25 March 1945).

Zamboanga had been the location of a bartering post between Chinese, Malays and native Filipinos as early as the 13^th century, and it was here that the Spanish founded a city in 1635. Zamboanga is located at the foot of the Basilan mountains, which reach a height of 4,380 ft (1335 m), and in the area of Zamboanga itself there is a narrow coastal plan with a reef and numerous coral heads off its shore. The city commands the Basilan Strait between Mindanao and Basilan island, and in its time was an important fishing port.

On 16 December 1941 Major General Shisuo Sakaguchi’s 'Sakaguchi' Detachment from the Palau islands group, with the headquarters of Sakaguchi’s 56^th Mixed Infantry Group, the 146^th Regiment and elements of some special naval landing forces, had landed at Davao on the south coast of eastern Mindanao. This force was detached from Lieutenant General Hitoshi Imamura’s 16^th Army otherwise concerned with the seizure of Borneo and Java. Landing with the 'Sakaguchi' Detachment was Lieutenant Colonel Toshio Miura’s 'Miura' Detachment comprising the 1/33^rd Regiment of Lieutenant General Susumi Morioka’s 16^th Division. Davao was defended by 2,000 Filipino troops, who were soon forced to withdraw. Lieutenant Colonel Matsumoto’s 'Matsumoto' Detachment departed on 23 December for the occupation of Jolo island on 24 December with the defeat of just 300 men of the Philippine Constabulary, but the 'Miura' Detachment remained to establish a seaplane base and bring the airfield outside Davao into operation. Both Davao and Jolo were then used as launch sites for the 'B' (ii) operation to take Borneo.

The Japanese made no effort to secure the entire island of Mindanao during the first months of 1942. The 'Miura' Detachment was contained at Davao and Digos, and the Filipino army units, assigned to a number of defence sectors through the island, continued to train. General Douglas MacArthur, the Allied commander-in-chief in the Philippine islands group, hoped that the US and Filipino forces would hold out on Mindanao until he was able to mount an offensive from Australia and use the island as a forward base for the reconquest of the rest of the Philippine islands group.

After securing Cebu island between Negros and Bohol islands on 29 April, Major General Kiyotake Kawaguchi’s 'Kawaguchi' Detachment (based on the 124^th Regiment) landed in the Moro Gulf on the central portion of Mindanao island’s west coast and advanced to the north as well as to the east, and the 'Miura' Detachment moved to the west from Digos to meet it.

Meanwhile, on 2 March elements of Rear Admiral Naosaburo Irifune’s 32^nd Base Force, totalling some 200 men, had seized the port of Zamboanga, on the north coast of the Zamboanga peninsula, and started to establish a seaplane base.

After taking Panay island, to the north-west of Negros, Major General Saburo Kawamura’s 'Kawamura' Detachment (based on the 41^st Regiment) landed at Cagayan in Macajalar Bay near the point at which Routes 1 and 3 joined on the central portion of the north coast.

When he surrendered his headquarters on Corregidor island on 7 May, Lieutenant General Jonathan M. Wainwright, currently commanding all the Allied forces in the Philippine islands group, had released Major General Frederick W. Sharp, to the command of MacArthur, now based in Australia, but on the night of 7 May attempted to reassume command to order Sharp’s Visayan-Mindanao Force to enforce the surrender he had signed, for Wainwright feared that the 11,000 surrendered troops on the fortified islands might be massacred if the southern forces did not meet Japanese demands. MacArthur had ordered Sharp to ignore Wainwright. A truce was arranged and meetings were held between Sharp and the Japanese. Once he had learned of the situation in the north from a staff officer sent by Wainwright, Sharp surrendered his forces on 10 May. Many of the more distant units were without communications, however, and some were already executing raids and harassing attacks on the occupying Japanese troops.

By a time early in 1945, the Japanese forces on Mindanao and the islands of the Sulu archipelago had come under the control of Lieutenant General Sosaku Suzuki’s 35^th Army headquartered on Cebu. The forces on Mindanao were divided into two separate commands because of the island’s size and shape, the boundary between the two sectors lying just to the east of Lake Lanao near the isthmus connecting the Zamboanga peninsula with the rest of Mindanao. The Zamboanga peninsula west of this dividing line was the responsibility of Major General Tokichi Hojo’s 54^th Independent Mixed Brigade (less detachments on other islands), and other units in the area were the 33^rd Guard Force as well as a number of army and navy air service units. The Japanese strength on the Zamboanga peninsula was a little less than 9,000 men.

The main position in the Sulu archipelago was on Jolo island, which was held by Major General Tersuzo Suzuki’s 55^th Independent Mixed Brigade with a strength of 3,000 men supplemented by 500 Japanese navy personnel.

The Japanese forces on the main part of Mindanao, to the east of the dividing line near Lake Lanao, were commanded by Lieutenant General Gyosaku Morozumi with 58,000 army and navy personnel. Morozumi later assumed nominal command of the 35^th Army after Sosaku Suzuki had been killed on 14 June. There were 17,000 Japanese civilians (including 5,000 conscripted labourers) in the area of Davao, the island’s principal city. Morozumi exercised direct control of his own Korean-manned 30^th Division (40^th Field Artillery Regiment, 74^th Regiment, and battalions of the 41^st and 77^th Regiments). Service and airfield units plus the headquarters of Lieutenant General Seiichi Terada’s 2^nd Air Division were also attached to the 30^th Division. These units were responsible for the defence of western and northern Mindanao.

Southern and eastern Mindanao were the responsibility of Lieutenant General Jiro Harada’s 100^th Division (75^th Brigade and 76^th Brigade), which was left largely to its own devices. Also under Harada�s command were air service and airfield units as well as Rear Admiral Naoji Doi’s 32^nd Special Base Force. Most of the service units attached to both divisions had been reorganised into combat units. The Japanese airfields in the area included six in the north-west at Patag, Lumbia, Del Monte, Malaybalay, Valencia and Dansalan; three around Davao at Licanan, Sasa and Matina; two on the tip of the Zamboanga peninsula; and Bongao on the south-western end of Tawi-Tawi island near the south-western end of the Sulu archipelago.

Already in action against these Japanese forces on Mindanao were Filipino guerrillas, who were well organised under the 10^th Military District headquartered at La Paz in the north-east and under the command of Colonel Wendell W. Fertig. The 38,000 guerrillas were well armed and organised into the 105^th Division (6,600 men), 106^th Division (3,900 men), 107^th Division (2,500 men), 108^th Division (15,000 men), 109^th Division (4,300 men) and 110^th Division (5,400 men) as well as the Maranao Militia Force (9,500 Moros). There were also 1,500 Moro guerrillas in the Sulu archipelago under the control of the Sulu Area Command.

It was during the day on which the 8^th Army was ordered to undertake the 'Victor V' invasion of Mindanao that the 41^st Division launched 'Victor IV' against Zamboanga at the same time that the rest of the division was undertaking the 'Victor III' recapture of Palawan island. The invasion force was transported from the eastern part of Mindanao in the ships of the Zamboanga Attack Group (Rear Admiral Forrest B. Royal’s Task Group 78.1), and faced Japanese forces which had established strong defensive positions around Zamboanga City at the southern tip of the peninsula.

The slow completion of the US airfield at Palawan posed a problem for the provision of tactical air support for 'Victor IV', but the seizure of a makeshift airstrip at Dipolog, in an area about 145 miles (235 km) to the north-east of Zamboanga City, by the guerrillas of the 105^th Division, allowed the Americans to exploit an extemporised opportunity for the aerial delivery of two reinforced companies of the 21^st Infantry of Major General Roscoe B. Woodruff’s 24^th Division to ensure control of the airstrip. Soon after this Colonel Clayton C. Jerome’s Marine Aircraft Group, Zamboanga, began to fly missions off the airstrip to cover the naval bombardment and landing preparations off Zamboanga City.

After the landing areas had been bombed by aircraft of Major General Paul B. Wurtsmith’s 13^th AAF and a three-day bombardment had been completed by warships of the US Navy, the 162^nd Infantry and 163^rd Infantry landed 3 miles (4.8 km) to the west of Zamboanga City. The headquarters ship for the 'Victor IV' landing was Rocky Mount, and the transport group comprised four troop-carrying destroyer conversions, one dock landing ship, 23 tank landing ships, 21 medium landing ships, 32 infantry landing craft and 17 support infantry landing craft, two patrol craft and two submarine chasers. The minesweeping group comprised 11 motor minesweepers and the Australian sloop Warrego, the escort comprised the destroyers Waller, Saufley, Philip, Sigourney, Robinson, McCalla, Bancroft and Bailey (Destroyer Squadron 22) and the destroyer escorts Rudderow and Chaffee, and preparatory gunfire bombardment and fire support were provided by Rear Admiral Russell S. Berkey’s TG74.3 comprising the light cruisers Phoenix and Boise, and destroyers Fletcher, Nicholas, Taylor, Jenkins and Abbot (Destroyer Squadron 21). Air support was provided by elements of Major General Ennis C. Whitehead’s 5^th AAF and Wurtsmith’s 13^th AAF.

As the assault force closed the beach, Japanese shore batteries sank LST-591, LST-626, LCI-710 and LCI-779, but the Japanese midget submarines Ha-78, Ha-79 and Ha-84 missed targets with their torpedoes. The Japanese opposition to the landings was then very limited, and the units of the 41^st Division quickly captured the city, which had been very severely damaged by the pre-invasion bombardments. On the following day, the US forces met strong resistance as they attacked the Japanese positions in the hills overlooking the coastal plain. For two weeks US infantry, very ably supported by US Marine Corps aircraft and US Navy gunfire, fought the Japanese along a 5-mile (8-km) front in terrain so difficult that the use of armour was impossible, and in positions heavily fortified with deep earth emplacements, barbed wire entanglements, minefields and booby traps.

On 23 March the centre of the Japanese position was finally broken, and during the next three days the 162^nd Infantry continued to eliminate the remnants of the Japanese resistance in this central sector. Replacing the 163^rd Infantry, the 186^th Infantry continued the attack and the 54^th Independent Mixed Brigade was compelled to withdraw a week later and, harassed by Filipino guerrillas, to retreat along the peninsula and into the jungle. Mopping up operations then completed the 'pacification' of the Japanese, who eked out an increasingly difficult and guerrilla-decimated existence for the rest of the war.

The campaign of the Zamboanga peninsula cost the US forces 220 men killed, and the Japanese 6,400 dead.

Two airfields were established at Calarian and Moret near Zamboanga to support the 'Victor V' attack on eastern Mindanao.

Alongside the Zamboanga operation, smaller units of the 41^st Division effected landings on the islands of the Sulu archipelago, which extend south-west from the Zamboanga peninsula to northern Borneo. Taken in a rapid succession were the islands of Basilan (16 March), Malamaui, Tawi-Tawi, Sanga-Sanga and Bangao. On 9 April, the US forces encountered strong resistance on Jolo. With their resistance anchored on Mt Dabo, some 3,900 Japanese held off the 163^rd Infantry supported by Filipino guerrillas. By 22 April, however, the position had fallen after hard fighting, and the remnants of the Japanese force pulled right back to hold out in the west of the island for a further two months. The 163^rd Infantry suffered 40 dead and 125 wounded by the middle of June, while some 2,000 Japanese troops died.